MacMartin, Douglas G.; Kravitz, Ben (2016): Multi-model dynamic climate
emulator for solar geoengineering. In Atmos. Chem. Phys. Discuss., pp.
1–14. DOI 10.5194/acp-2016-535.
www.atmos-chem-phys-discuss.net/acp-2016-535/
Climate emulators trained on existing simulations can be used to project
the climate effects that would result from different possible future
pathways of anthropogenic forcing, without relying on general
circulation model (GCM) simulations for every possible pathway. We
extend this idea to include different amounts of solar geoengineering in
addition to different pathways of green-house gas concentrations by
training emulators from a multi-model ensemble of simulations from the
Geoengineering Model Intercomparison Project (GeoMIP). The emulator is
trained on the abrupt 4 x CO_2 and a compensating solar reduction
simulation (G1), and evaluated by comparing predictions against a
simulated 1 % per year CO_2 increase and a similarly smaller solar
reduction (G2). We find reasonable agreement in most models for
predicting changes in temperature and precipitation (including regional
effects), and annual-mean Northern hemisphere sea ice extent, with the
difference between simulation and prediction typically smaller than
natural variability. This verifies that the linearity assumption used in
constructing the emulator is sufficient for these variables over the
range of forcing considered. Annual-minimum Northern hemisphere sea ice
extent is less-well predicted, indicating the limits of the linearity
assumption. For future pathways involving relatively small forcing from
solar geoengineering, the errors introduced from nonlinear effects may
be smaller than the uncertainty due to natural variability, and the
emulator prediction may be a more accurate estimate of the forced
component of the models' response than an actual simulation would be.
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